This invention relates generally to a fluid pump. More particularly it relates to a gear pump having provisions for the relief of fluid trapped due to action of the gear teeth during normal pump operation.
During normal operation of a gear pump, the gear teeth move into meshing engagement, thereby creating cavities between the points of contact of adjacent pairs of meshing teeth. Engagement is along a line of action extending through the pitch point of the gears. Fluid is trapped in the cavities, and is subject to pressure changes as cavity volume changes.
At the point of initial tooth contact, the cavity is in fluid communication with the pump outlet. As this initial tooth contact approaches the minimum land position, the volume of the cavity is reduced and fluid communication with the outlet is interrupted. When the cavity volume is at a minimum, the squeezed pressure of fluid within the cavity is at a maximum. Thereafter, as the teeth continue to move during normal operation, cavity volume increases with a corresponding decrease in squeezed pressure. As the teeth approach the point where tooth contact is broken, fluid communication is established between the cavity and the pump inlet.
The prior art discloses various examples of pressure plates having inlet and outlet recesses designed to relieve squeezed pressures, either to the outlet or inlet, or in some cases to both. However, a common feature of the prior art is that direct communication with the recesses is interrupted as the teeth move through the minimum land position. Pumps heretofore have been designed to establish a fluid seal at some point for the purpose of reducing leakage and thereby minimizing any reduction in volumetric efficiency. A problem common to such prior art pumps is the high level of hydraulic noise. There remains a need in the art for a gear pump having apparatus for suppressing excessive hydraulic noise without at the same time causing an unacceptable reduction in volumetric efficiency.